Stormwater runoff, including urban, industrial, and agricultural stormwater runoff, is a major component of non-point source pollution and the primary cause of combined wastewater treatment facility overflows. Excessive runoff volumes laden with ionic species, such as nutrients containing nitrate, phosphate and chloride ions, are of concern due to their persistence in the environment and toxicity to humans and ecosystems. Accordingly, there is a definite need for an improved method for reducing such pollutants in stormwater runoff.
Conventional bioretention systems that include soil filter media, such as vegetated buffers, rain gardens and constructed wetlands, are designed to treat runoff by employing filtration, deposition, adsorption and infiltration through porous media. However, it is a drawback of these systems that they have limited long-term effectiveness due to the limited treatment capacity of the soil filter media. Accordingly, there is also a definite need for a soil filter additive that improves the long term effectiveness of bioretention systems.